Distributed Wireless Charging System and Method

ABSTRACT

A distributed wireless radio frequency-based charging system includes hardware and software platforms. The hardware platform includes adaptive energy harvesters and programmable energy transmitters. The software platform manages the hardware profiles, resources (e.g., energy waveforms and transmission powers), schedules the beams of the energy transmitters, and switches between modes of wireless charging and data access point. This allows the energy transmitters to be configured adaptively based on the ambient energy availability, energy needs and number of energy-requesting devices in the network. Under the software control, the energy transmitters can cooperatively form focused beams of energy and power for transmission to energy harvesters in the energy-receiving devices, such as sensors, Internet of Things (IoT) enabled appliances, and mobile/wearable equipment. The energy harvesters can utilize the energy contained within the transmitted beams, as well as ambient RF sources, for directly powering their operation or charging a battery/capacitor for subsequent use.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 120 of U.S.application Ser. No. 16/078,742, filed on 22 Aug. 2018, entitled“Distributed Wireless Charging System and Method,” which is a nationalstage entry under 35 U.S.C. § 371 of PCT/US2017/022106, filed on 13 Mar.2017, entitled “Distributed Wireless Charging System and Method”, whichclaims priority under 35 § 119(e) of U.S. Provisional Application No.62/308,298, filed on 15 Mar. 2016, entitled “Software-Defined ControlPlane for Distributed Wireless Energy Transfer System,” the disclosuresof all of which are hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention was developed with financial support from Grant No.1452628 from the National Science Foundation. The U.S. Government hascertain rights in the invention.

BACKGROUND

Some estimates suggest that the number of connected devices worldwidewill increase to 50-200 billion by 2020, with global spending reaching1.7 trillion in that same year. Connected devices are used at multiplelevels of society, from a personal level (for example, wearable devices)to a community level (for example, smart cities). In addition, energyconsumption demands are increasing exponentially due to the developmentof processor-heavy applications, higher data communication rates andtechnologies, and increased usage of multimedia content. On the otherhand, battery technology is constrained by limited space and iscurrently unable to keep up with the expansion of power needs.Replenishment and maintenance of batteries are costly and critical todevice performance. Battery-related issues are a main concern inmilitary, consumer, and commercial markets.

Wireless energy transfer is useful for charging rechargeable batteries,such as batteries used in sensors and mobile devices. Commerciallyavailable wireless charging systems have limitations such as lowcharging rates, need for line-of-sight alignment, and close contact withthe device to be charged.

SUMMARY OF THE INVENTION

A method and system are provided to transfer energy wirelessly to powerdevices by employing distributed energy beam forming, ambient RF energyharvesting, or a combination thereof.

In some embodiments, a controllable, programmable distributed wirelessradio frequency (RF)-based charging system and method are provided thatinclude and utilize both hardware and software platforms. The hardwareplatform includes programmable energy transmitters (ETs) and adaptiveenergy harvesters coupled with energy-receiving target devices. Thesoftware platform remotely manages the hardware profiles and resources(e.g., energy waveforms and transmission powers), schedules energytransmissions from the energy transmitters, and commands switching ofthe ETs between two modes of RF energy transmission for wirelesscharging and data access point for data communication. This allows theenergy transmitters to be configured adaptively based on the ambientenergy availability, energy needs and number of energy-requesting targetdevices in a network. Under the software control, the energytransmitters can cooperatively form focused beams of energy to transmitpower to a set of target devices using radio frequencies within, forexample, a license-free industrial, scientific and medical (ISM) band.The energy-receiving target devices, such as sensors, Internet of Things(IoT) enabled appliances, and mobile and/or wearable equipment that arecoupled with the adaptive energy harvesters, can utilize the energycontained within the transmitted beams, as well as ambient RF sources,for directly powering their operation or for charging a battery and/orcapacitor for subsequent use. The coupled software and hardwareplatforms can flexibly monitor a wide range of areas, build live energymaps, estimate future energy demands, establish energy and datacommunications with devices, facilitate interoperability among devices,and detect and/or localize new devices within a coverage area.

Other aspects of the method and system include the following:

1. A method for distributed wireless charging, comprising:

in a network comprising at least two spatially distributed energytransmitters, an energy receiving target device, and a controllercomprising one or more processors and memory, and machine readableinstructions stored in the memory executable by the one or moreprocessors, the steps of:

receiving, at the controller, a communication from the energy receivingtarget device or from one of the energy transmitters comprising a needfor energy by the energy receiving target device; and

transmitting, by the controller to the at least two energy transmitters,instructions for wireless transmission of radio frequency (RF) energyfrom the at least two energy transmitters to the energy harvestingtarget device.

2. The method of embodiment 1, further comprising:

transmitting RF energy to form constructive interference at the energyharvesting target device by the at least two energy transmitters; and

converting energy contained in the RF energy into electrical energy byenergy harvesting circuitry in the energy harvesting target device forimmediate use or for storage.

3. The method of any of embodiments 1-2, wherein each of the energytransmitters is operative to adjust one or more of a frequency, a phase,and a time of transmission of the RF energy to form constructive energybeams at the energy harvesting target device.4. The method of any of embodiments 1-3, wherein the instructionstransmitted by the controller include one or more of a power level to betransmitted, a duration of transmission, an identification of the energyreceiving target device, and a schedule of transmission.5. The method of any of embodiments 1-4, wherein the instructionstransmitted by the controller include one or more of switching theenergy transmitters on and off, changing a power level transmitted byeach of the energy transmitters, and changing a duration of energytransmission of each of the energy transmitters.6. The method of any of embodiments 1-5, wherein the instructionstransmitted by the controller include active data communicationprotocols, the communications protocols including at least WiFi, ZigBee,and Bluetooth protocols; a role of each energy transmitter, the rolesincluding an energy transfer mode and a data access point communicationmode; and a duration of the roles of the energy transmitters.7. The method of any of embodiments 1-6, further comprisingtransmitting, from the energy harvesting target device to one or more ofthe energy transmitters or to the controller, an indication of one ormore of an energy discharging rate, an ambient RF energy harvestingrate, or an energy storage level at the energy harvesting target device.8. The method of any of embodiments 1-7, further comprising transmittingfeedback, from the energy harvesting target device to one or more of theenergy transmitters, comprising an indication of a received signalstrength from the energy transmitters or channel estimations.9. The method of any of embodiment 8, further comprising, in response tothe feedback, iteratively adjusting one or more of frequency, phase, ortiming of the RF energy from one or more of the energy transmitters tooptimize constructive interference at the energy harvesting targetdevice.10. The method of any of embodiments 1-9, wherein the energy harvestingtarget device further harvests RF energy from an ambient RF source.11. The method of embodiment 10, wherein the ambient RF source isharvested from radio signals, cellular signals, global system for mobile(GSM) signals, or digital or analog television signals.12. The method of any of embodiments 1-11, wherein the energy receivingtarget device is one of a set of multiple energy receiving targetdevices in the network, and the instructions include schedulingtransmissions of energy over time to each of the energy receiving targetdevices.13. The method of any of embodiments 1-12, wherein the energy receivingtarget device is one of a set of multiple energy receiving targetdevices in the network, and the controller is operative to apportionenergy transmission between multiple ones of the energy harvestingtarget devices based on current energy levels of each energy harvestingtarget device, a number of the energy harvesting target devices, and anestimated future energy demand.14. The method of any of embodiments 1-13, wherein the energy receivingtarget device is one of a set of multiple energy receiving targetdevices in the network, and the controller is operative to register,authenticate or track a location of each of the multiple energyharvesting target devices.15. The method of any of embodiments 1-14, wherein the energy receivingtarget device is one of a set of multiple energy receiving targetdevices in the network, and the controller includes an energy map storedin the memory, the energy map comprising an updatable compilation ofpresent and historical energy levels of the multiple energy harvestingtarget devices.16. The method of any of embodiments 1-15, further comprising switchingeach of the energy transmitters between an energy transmission mode anda data communication mode.17. The method of any of embodiments 1-16, wherein each of the energytransmitters comprises a software-defined radio configurable bycommunications from the controller, and an antenna in communication withthe software-defined radio.18. The method of any of embodiments 1-17, wherein one or more of theenergy transmitters further comprise a data access point or a gatewayfor the network.19. The method of any of embodiments 1-18, wherein the energy harvestingtarget device is a sensor, an Internet of Things-enabled device orappliance, a mobile device, an air-borne device, a wearable device, animplantable device, or a computing device.20. The method of any of embodiments 1-19, wherein the energy harvestingtarget device includes energy harvesting circuitry operative to convertenergy contained in RF energy into electrical energy for immediate useor for storage.21. The method of embodiment 20, wherein the energy harvesting circuitryincludes an antenna, a DC voltage rectifier in communication with theantenna, and an energy storage device in communication with the DCvoltage rectifier.22. The method of any of embodiments 20-21, wherein the energyharvesting circuitry includes a stage optimized for high RF to DCconversion efficiency for low input power levels and a stage optimizedfor high input power levels.23. The method of any of embodiments 20-22, wherein the energyharvesting circuitry includes impedance matching circuitry to optimizeRF to DC conversion efficiency over a desired frequency range.24. The method of any of embodiments 20-23, wherein the energy storagedevice comprises a battery or a capacitor.25. A system for distributed wireless charging, comprising:

a network comprising at least two spatially distributed energytransmitters, an energy receiving target device, and a controllercomprising one or more processors and memory, and machine readableinstructions stored in the memory executable by the one or moreprocessors, the controller operative to carry out operations comprising:

receiving a communication from at least one energy harvesting targetdevice; and

transmitting to at least two energy transmitters instructions forwireless transmission of radio frequency energy from the at least twoenergy transmitters to the energy harvesting target device.

26. The system of embodiment 25, wherein the controller is operative totransmit instructions including one or more of a power level to betransmitted, a duration of transmission, an identification of the energyreceiving target device, and a schedule of transmission.27. The system of any of embodiments 25-26, wherein the controller isoperative to transmit instructions including one or more of switchingthe energy transmitters on and off, changing a power level transmittedby each of the energy transmitters, and changing a duration of energytransmission of each of the energy transmitters.28. The system of any of embodiments 25-27, wherein the controller isoperative to transmit instructions including active data communicationprotocols, the communications protocols including at least WiFi, ZigBee,and Bluetooth protocols; a role of each energy transmitter, the rolesincluding an energy transfer mode and a data access point communicationmode; and a duration of the roles of the energy transmitters.29. The system of any of embodiments 25-28, wherein each of the energytransmitters is operative to adjust one or more of a frequency, a phase,and a time of transmission of the RF energy to form constructive energybeams at the energy harvesting target device.30. The system of any of embodiments 25-29, wherein each of the energytransmitters comprises a software-defined radio configurable bycommunications from the controller, and an antenna in communication withthe software-defined radio.31. The system of any of embodiments 25-30, wherein one or more of theenergy transmitters further comprise a data access point or a gatewayfor the network.32. The system of any of embodiments 25-31, wherein one or more of theenergy transmitters is operative to optimize constructive interferenceat the energy harvesting target device in response to the feedback, byiteratively adjusting one or more of frequency, phase, or timing of theRF energy.33. The system of any of embodiments 25-32, wherein the energy receivingtarget device includes energy harvesting circuitry operative to convertenergy contained in the RF energy into electrical energy for immediateuse or for storage.34. The system of embodiment 33, wherein the energy harvesting circuitryincludes an antenna, a DC voltage rectifier in communication with theantenna, and an energy storage device in communication with the DCvoltage rectifier.35. The system of embodiment 34, wherein the energy storage devicecomprises a battery or a capacitor.36. The system of any of embodiments 33-35, wherein the energyharvesting circuitry includes a stage optimized for RF energy conversionefficiency at low input power levels and a stage optimized for RF energyconversion efficiency at high input power levels.37. The system of any of embodiments 33-36, wherein the energyharvesting circuitry includes impedance matching circuitry to optimizeRF energy conversion efficiency over a desired frequency range.38. The system of any of embodiments 25-37, wherein the energyharvesting target device is operative to further harvest RF energy froman ambient RF source.39. The system of embodiment 38, wherein the ambient RF source isharvested from radio signals, cellular signals, global system for mobile(GSM) signals, or digital or analog television signals.40 The system of any of embodiments 25-39, wherein the energy harvestingtarget device is operative to transmit, to one or more of the energytransmitters or to the controller, an indication of one or more of anenergy discharging rate, an ambient RF energy harvesting rate, or anenergy storage level at the energy harvesting target device.41. The system of any of embodiments 25-40, the energy harvesting targetdevice is operative to transmit, to one or more of the energytransmitters, feedback comprising an indication of a received signalstrength from the energy transmitters or channel estimations.42. The system of any of embodiments 25-41, wherein the energy receivingtarget device is one of a set of multiple energy receiving targetdevices in the network, and the controller is operative to transmitinstructions including scheduling transmissions of energy over time toeach of the energy receiving target devices.43. The system of any of embodiments 25-42, wherein the energy receivingtarget device is one of a set of multiple energy receiving targetdevices in the network, and the controller is operative to apportionenergy transmission between multiple ones of the energy harvestingtarget devices based on current energy levels of each energy harvestingtarget device, a number of the energy harvesting target devices, and anestimated future energy demand.44. The system of any of embodiments 25-43, wherein the energy receivingtarget device is one of a set of multiple energy receiving targetdevices in the network, and the controller is operative to register,authenticate or track a location of each of the multiple energyharvesting target devices.45. The system of any of embodiments 25-44, wherein the energy receivingtarget device is one of a set of multiple energy receiving targetdevices in the network, and the controller includes an energy map storedin the memory, the energy map comprising an updatable compilation ofpresent and historical energy levels of the multiple energy harvestingtarget devices.46. The system of any of embodiments 25-45, wherein the energyharvesting target device is a sensor, a sensor mote, an Internet ofThings-enabled device or appliance, a mobile device, an air-bornedevice, a wearable device, an implantable device, or a computing device.47. A control system for distributed wireless charging, comprising:

a controller comprising one or more processors and memory, andmachine-readable instructions stored in the memory that, upon executionby the one or more processors cause the system to carry out operationscomprising:

receiving a communication from at least one energy harvesting targetdevice; and

transmitting to at least two energy transmitters instructions forwireless transmission of radio frequency energy from the at least twoenergy transmitters to the energy harvesting target device.

48. The control system method of embodiment 47, wherein the controlleris operative to transmit instructions including one or more of a powerlevel to be transmitted, a duration of transmission, an identificationof the energy receiving target device, and a schedule of transmission.49. The control system any of embodiments 47-48, wherein the controlleris operative to transmit instructions including one or more of switchingthe energy transmitters on and off, changing a power level transmittedby each of the energy transmitters, and changing a duration of energytransmission of each of the energy transmitters.50. The control system any of embodiments 47-49, wherein the controlleris operative to transmit instructions including use of one or more ofactive data communication protocols, the communications protocolsincluding at least WiFi, ZigBee, and Bluetooth protocols; a role of eachenergy transmitter, the roles including an energy transfer mode and adata access point communication mode; and a duration of the roles of theenergy transmitters.51. The control system of any of embodiments 47-50, wherein thecontroller is operative to transmit instructions including schedulingtransmissions of energy over time to multiple energy receiving targetdevices.52. The control system of any of embodiments 47-51, wherein thecontroller is operative to transmit instructions to apportion energytransmission between multiple energy harvesting target devices based oncurrent energy levels of each energy harvesting target device, a numberof the energy harvesting target devices, and an estimated future energydemand.53. The control system of any of embodiments 47-52, wherein thecontroller is operative to register, authenticate or track a location ofeach of multiple energy harvesting target devices.54. The control system of any of embodiments 47-53, wherein thecontroller includes an energy map stored in the memory, the energy mapcomprising an updatable compilation of present and historical energylevels of multiple energy harvesting target devices.

DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic diagram of an embodiment of a software-defineddistributed wireless charging system for three applications;

FIG. 2 is a schematic illustration of an embodiment software-definedbeamforming methodology;

FIG. 3A is a schematic illustration of a single energy transmitterillustrating crests and troughs of transmitted energy waves;

FIG. 3B is a schematic illustration of how multiple energy transmitterstransmitting at the same frequency and random initial phases can canceltransferred energy in destructive areas and aggregate energy inconstructive areas;

FIG. 4 is a schematic illustration of one embodiment of adjustableambient RF energy harvesting circuitry;

FIG. 5 is a block diagram of an embodiment of a software controller;

FIG. 6 is a block diagram of an embodiment of a programmable ET;

FIG. 7 is a block diagram of an embodiment of an energy harvestercoupled with a receiver device;

FIG. 8 illustrates a flow chart of an embodiment of a process ofET/device registration;

FIG. 9 illustrates a flow chart of an embodiment of a process ofadaptive energy allocations based on RF ambient power and dischargingrate changes;

FIG. 10 illustrates a flow chart of an embodiment of a process of systemadaptations to device movements and wireless channel changes;

FIG. 11 is a diagram of an example application of an embodiment foroffice/commercial building charging;

FIG. 12 is a diagram of an example application of an embodiment forhealthcare and medical device charging;

FIG. 13 is a diagram of an example application of an embodiment forInternet of Things (IoT) charging;

FIG. 14A is an illustration of an embodiment of a prototype system;

FIG. 14B is a graph illustrating a received power comparisondemonstrating energy beamforming with the prototype of FIG. 14A;

FIG. 14C is a graph comparing instantaneous harvested voltages forbeamforming and non-beamforming scenarios using the prototype of FIG.14A;

FIG. 15 is a graph illustrating experimental results on the effect ofdestructive and constructive energy interference for two energytransmitters (ET1 and ET2) when the distance between ET1 and thereceiver is set to 1 m;

FIG. 16 illustrates a dual stage RF energy harvesting prototype;

FIG. 17 is a schematic illustration of a Dickson multiplier used in theprototype of FIG. 16;

FIG. 18 is a schematic overview of an adjustable ambient RF energyharvesting system;

FIG. 19 is an illustration of a further ambient RF energy harvestingcircuit prototype;

FIG. 20 illustrates percentages that each ambient channel won thehighest measured power over Boston subway stations;

FIG. 21 illustrates the spatial diversity of measured ambient RF powersover seven Boston MBTA stations;

FIG. 22A illustrates a comparison of charging times for three scenarios(ET with no ambient harvesting, ET and LTE 730 MHz harvesting, and ETand GSM 850 MHz harvesting) over varying ET distances and ET EIRP equalto 1;

FIG. 22B illustrates a comparison of charging times for three scenarios(ET with no ambient harvesting, ET and LTE 730 MHz harvesting, and ETand GSM 850 MHz harvesting) over varying ET EIRPs and ET distance equalto 2 m;

FIG. 23 illustrates levels of average RF power over a set of places suchas a subway station, university, museum, shopping center, and park inBoston; and

FIGS. 24A and 24B illustrate improvements of distributed beamforming interms of charging ranges (FIG. 24A) and harvesting rates (FIG. 24B).

DETAILED DESCRIPTION OF THE INVENTION

This application incorporates by reference the entire disclosure of U.S.Provisional Application No. 62/308,298, filed on Mar. 15, 2016, entitled“Software-Defined Control Plane for Distributed Wireless Energy TransferSystem.”

In some embodiments, a system and method include multiple programmableenergy transmitters (ETs) distributed over a network to create andtransmit beams of electromagnetic RF energy toward determined targetdevices in need of charging. The target devices include energyharvesters operable to receive the RF energy and convert it toelectrical energy to charge or power the target device. A softwareplatform provides various functionalities, such as, for example,managing the hardware resources, scheduling the energy beams, andswitching between ET/access point roles.

For example, in some embodiments, various software-implemented modulescan be provided at a controller or at the various ETs. Such modules canimplement functionalities such as distributed energy beamforming toensure adaptive and high coverage wireless charging rates; energy wavemanagement for scheduling energy streams and constant monitoring ofwireless charging progress; and reliable data and energy communicationfor the control aspects of requesting energy, registration andauthentication of target devices, monitoring energy requirements oftarget devices, switching between energy transmission and datacommunication modes, and management of wireless standard compatible datacommunications over the network. Distributed energy beamforming caninclude features such as i) frequency, phase, and time synchronization,ii) localizing receivers, iii) managing a set of energy target devices,and iv) coordination of energy streams among a set of ETs.

In some embodiments, distributed wireless charging can include sendingregistration notifications from devices to the ETs and/or the controllerthrough a local network or the Internet, registering and authenticatingthe devices at the controller, allocating resource parameters thatdefine RF energy wave shapes, selecting an optimal subset of theavailable ETs in proximity to the energy requesting target devices, andscheduling and focusing of energy beams based on the current energystatus of target devices in the network (including battery levels, thenumber of active target devices that have requested charging, andestimated future energy demands), sending configuration commands fromthe controller to the programmable ETs, transmitting the RF beams fromdistributed ETs to target devices based on determined schedules,capturing the energy beams by an energy harvester in the target device,and converting the incident RF energy into electrical energy for storageacross a capacitor and/or battery or for immediate use, sending feedbackfrom target devices to the ETs for phase and frequency correction of theenergy beams, updating the energy and traffic status with energy updatepackets from a target device to the controller, creating visualizationsof live energy maps at the controller to estimate future demands, anddetecting a new energy requesting device in a coverage area by ETs.

In some embodiments, the energy harvester can include multi-bandharvesting circuitry that harvests both controlled energy beams from theETs and ambient RF energy.

In some embodiments, the ETs can have dual roles, as an energytransmitter and as a data access point. They can switch between anenergy beamforming mode and a data communications mode, where in thelatter mode, the ET can act as an access point/gateway for wirelessstandards compatible data communications such as WiFi, ZigBee, andBluetooth. In the access point mode, the ETs can be responsible forcommunication, can exchange information through baseband digitalpackets, and can enable the interoperability of data communication amongdevices. In some embodiments, the ETs can have dual transceivers foroperation simultaneously in the energy transmission mode and datacommunications mode.

In some embodiments, a dynamic and anticipatory energy scheduling can beemployed. For example, target devices can have spatially and temporallyvarying energy needs based on their application-specific requirements.These different energy needs may benefit from different energy waveallocations, tailored to each specific device. The controller can usethe latest aggregated energy updates and status of target devices toschedule the duration and transfer power from ET beams and can accountfor harvesting energy by the target devices from ambient RF sources tosupport current energy needs. Furthermore, anticipatingapplication-specific traffic demands (based on node-initiated “energyreports” and live energy maps), the controller can direct the local ETsto provide power and charging times that are adequate to supportestimated future energy needs.

In some embodiments, the system and method can provide distributedwireless charging from multiple ETs to one or more target devices whileeliminating the need for contact-based or wireline charging, which maynot be accessible or easy to use or which may make the target devicesunusable during charging.

FIG. 1 illustrates a system overview of an embodiment of the presentinvention for distributed software-implemented wireless RF energytransmission to power electronic target devices. The target devicesshown here can be any devices that are powered by electricity, such as,without limitation, a sensor or sensor mote, an Internet ofThings-enabled device or appliance, a mobile device, a wearable device,an implantable device, an air-borne device, or a computing device. Suchdevices can include, without limitation, mobile phones, laptops, clocks,watches, temperature sensors, thermostats, and the like. Air-bornedevices can include, without limitation, drones or unmanned aerialvehicles, powered airplanes, satellites, and the like.

The embodiment includes a software-implemented controller chain, from acontroller 101 in communication with programmable energy transmitters(ETs or PETs) 103. In some embodiments, the controller can beimplemented as or with a server. A distributed energy beamformingparadigm allows multiple distributed ETs to charge target devices 104from a distance. A wireless access point mode allows ETs to switch to adata communication role to transmit/receive data to and from devicescompatible with wireless standards. A power reception chain includesenergy harvesters coupled to target devices for powering the targetdevices. In some embodiments, programmable ETs within each charging areacan be connected to the controller through a commercially available WiFiaccess point (AP) 102. In some embodiments, the ETs can be pluggeddirectly into regular electrical sockets or outlets of a power systemof, for example, a building. In some embodiments, the ETs can behardwired directly into the power system. In some embodiments, the ETscan be mounted externally on walls and/or ceilings.

The controller can build a database of knowledge of the network throughfeedback from the ETs and/or the target devices and can subsequentlymanage the energy waves emitted by the ETs by sensing re-configurationcommands and intelligent beam scheduling. The distributed ETs cangenerate coordinated RF beams toward the target devices sequentiallybased on a schedule from the controller. The energy harvester in thetarget device may use the energy beams, as well as ambient RF energy,for replenishing the energy storage, for example, in a capacitor orbattery, thereby allowing the device to run without batteryreplacements. The controller can perform similar energy transferoptimizations for a large number of deployment scenarios, alsoconsidering any global interference scenarios between groups of ETscontrolled by different users or installed by distinct establishments.The set of target devices that are served at any given time, and theschedules of the distributed energy beams can change adaptively, basedon the energy demands and energy status of a network notified to thesoftware controller. In some embodiments, the ETs can switch to a dataaccess point mode where each ET can communicate independently with oneor more devices to exchange digital packets. Three example applicationsthat are shown in FIG. 1 are an office/commercial building 200, a bodyarea network 300 including sensors connected to a human subject formonitoring the body/health conditions, and an Internet of Things (IoT)scenario 400 with multiple appliances in a smart home.

Referring to FIG. 2, in some embodiments, a system includes a set ofprogrammable ETs, RF-energy harvesting circuits at each target device,and a controller with controlling software. The controller manages theenergy-related resources such as transmit power, beam durations, activetargeted device(s), and beam schedules, while feedback from the devicescan be used by each ET independently for frequency, time, and phasesynchronization to form constructive energy beams. The system can haveany desired number n of ETs with independent frequency and clockreferences to transfer RF waves that combine at a receiverconstructively. In some embodiments, a transmit antenna at each ET canbe connected to an independent software defined radio, with its owncrystal oscillator that regulates timing. Different oscillatorsnaturally have different frequency and phase shifts with respect to eachother, which also drift over their operation time. On the other hand, ina network with multiple ETs, the RF waves can combine constructively anddestructively over the space based on the initial transmission phase,wireless channel, and relative distance of participating ETs. Due tothis complexity and the nature of RF signals, the amount of receivedpower from multiple ETs is not a simple superposition of the individualvalues, but the summation of received signals in phasor form.

FIGS. 3A and 3B illustrate how concurrent energy transmissions at thesame frequency cancel the transferred energy in destructive areas andaggregate energy in constructive areas. FIG. 3A illustrates atwo-dimensional pattern of transferred energy produced by a single ET,and FIG. 3B illustrates a two-dimensional pattern of transferred energyproduced by multiple ETs, showing the areas of constructive anddestructive interferences.

The programmable ET can each include a Universal Software RadioPeripheral (USRP) connected to a power amplifier. The USRPs canimplement a beamforming algorithm for phase and frequencysynchronizations and can transfer high power energy signals toward thedesired target device using the power amplifier with maximum allowablepower under FCC rules. Using distributed energy beamforming, the ETs canself-adjust their phase based on feedback from the target device, sothat maximum net energy is transferred towards the intended targetdevice. In particular, the ETs can organize themselves into a virtualantenna array and focus their transmission energy in the direction ofthe target device, such that the emitted waveforms add up constructivelyat the target device. Each ET can use Kalman filtering techniques, suchas an extended Kalman filter, to estimate and correct the frequencyoffset between its carrier frequency and the feedback as referencesignal.

The target devices include energy harvesting circuitry that can convertthe incident RF energy into a DC voltage stored in a storage device,such as a battery or capacitor or for immediate use. In someembodiments, the RF-energy harvesting circuit at each target device caninclude an antenna for receiving incoming RF energy, a DC voltagerectifier, and an energy storage device, such as a capacitor or battery,to receive a DC voltage from the voltage rectifier. An impedancematching circuit can be provided between the antenna and the voltagerectifier to maximize the energy transfer and minimize power reflectionbetween the antenna and the voltage rectifier. A tunable impedancematching network can allow the optimal operating frequency range to beadjusted to maximize RF to DC conversion efficiency over any desiredfrequency range without a need for new circuitry fabrication.

In some embodiments, the sensor can estimate the received signalstrength (RSS) of the net incoming signal and broadcast a single bit toall the ETs to indicate whether this value is higher or lower than thatmeasured in the previous time slot. If the RSS is higher, the ETs canupdate this information and perturb their phase setting using the lastsetting as the baseline. If the RSS is lower, the ETs can revert theirphase selection to that of the previous time slot, before beginning thesubsequent round of phase perturbation. This randomized ascent procedureis repeated until the ETs converge to phase coherence. There is asynchronization period for phase adjustments among ETs, where the systemconverges to an optimal value in a few seconds time using thesensor-generated feedback.

In some embodiments, the target devices can include energy harvestingcircuitry to harvest ambient RF energy from RF sources such as, withoutlimitation, radio signals, cellular signals, global system for mobile(GSM) signals, or digital or analog television signals. FIG. 4illustrates a schematic overview of an embodiment of an adjustableambient RF energy harvesting device 104. The components include anantenna 120, an impedance matching network 122, a voltage multiplier124, and energy storage 126. The incident RF power is converted into DCpower by the voltage multiplier. The impedance matching network, whichcan include inductive and capacitive elements, provides a maximum powerdelivery from the antenna to the voltage multiplier. The energy storageprovides smooth power delivery to the load and provides a reserve fordurations when external energy is unavailable. The number of multiplierstages is selected to optimize performance. For example, increasing thenumber of multiplier stages gives higher voltage at the load, yetreduces the current through the final load branch. This may result inunacceptable charging delays for the energy storage capacitor.Conversely, fewer multiplier stages can provide more rapid charging ofthe capacitor, but the voltage generated across it may be insufficientto drive the device, such as a sensor mote. Similarly, a slight changein the matching circuit parameters can alter significantly the frequencyrange in which the efficiency of the energy conversion is a maximum, insome cases by several MHz. Thus, the RF harvesting circuitry can bedesigned in consideration of the optimum choices for a particularapplication.

In some embodiments, the controller can determine an appropriate time toswitch an ET's role from wireless energy transfer to data communicationand vice versa. The described distributed energy beamforming allows ETsto emulate a software-defined and scalable virtual multiple-inputmultiple output (MIMO) system that can transmit N concurrent streams toone or more devices that can give an improvement of N² in the gain ofthe received power. More generally, some or all of the multiple ETs andall or some of devices can have multiple antennas. A new device canregister and authenticate itself to the controller before receivingenergy, and can be automatically localized by ETs within its networkdepending upon the number of ETs that are within its range. The chargingtarget devices can send energy updates to the controller over time,informing about the change in their energy demands, and the controllercan issue reconfiguration commands to satisfy the energy needs of thenetwork based on the energy updates.

FIG. 5 illustrates a component level embodiment for a controller 101,which can be utilized to adaptively control the ETs and providedistributed wireless charging as described in FIG. 1. The controller caninclude various software-implemented modules, such as query management130, registration/authentication 132, power management 134, energyestimation 136, energy maps 138, beam scheduling 140, energy/data roleswitching 142, and device tracking 144. The query management module canreceive and process queries such as registration/authentication oftarget devices and energy updates from target devices and also relay theconfiguration commands and tracking queries. The power management modulecan allocate optimal resources within ETs, such as transmission power,duration, and targeted devices for charging. Upon reception of energyupdates, the query management module forwards them to the powermanagement module, which then builds the latest energy map of thenetwork. These maps capture the latest energy status and recent historyof energy needs for each target device. The energy estimation module canuse the energy maps to estimate future energy demands. The energy mapsand energy estimations can be given to the beam scheduling module, whichoptimizes the scheduling of energy beams to satisfy the new energydemands. The energy map can also be returned to a user for viewingpurposes. The power management module can send the reconfigurationcommands through the query management module to the ETs. The trackingmodule can send tracking packets to ETs for localizing a new device uponreceipt of a registration or authentication query and when changes in adevice location are detected. The data/energy role switching module candecide to send commands to an ET to switch its role between energytransmitter and data access point.

FIG. 6 illustrates the component level embodiment for a programmable ET103, which can be used for transferring RF power toward the desiredelectronic devices. A programmable ET can include varioussoftware-implemented modules, such as a command manager 150, hardwareprofile updater 152, energy wave manager 154, feedback manager 158,phase sync 160, frequency sync 162, LO estimator 164, query manager 166,Rx localizer 168, and data manager 170. The ET processes any commandsfrom the controller 101 by the command manager module and passes therequested updates in transmission power, duration, and beam schedulesfor each active target device 104 to the hardware profile updater thatkeeps and manages the hardware-related parameters. Feedback from atarget device can be processed through the feedback manager module,which, in turn, connects to the local oscillator (LO) estimator,frequency sync, and phase sync modules for adjusting/correcting theerrors local frequency and phase of ET to create constructiveinterference at the receiver of the target device. The query manager inthe ET can be used for passing the energy updates from the target deviceto the controller and also process tracking requests from thecontroller. The energy wave manager allocates beam streams according tothe received commands from the controller, including beam schedules,updated hardware profiles, adjusted frequency, and adjusted phase. Thedata manager is responsible for implementing the functions of protocolspecific data communications, e.g., WiFi, ZigBee, and Bluetooth, toexchange data packets when the controller changes the ET's role to anaccess point.

FIG. 7 illustrates a component level embodiment for an integratedmulti-band energy harvester coupled with a receiver at a target device104 that can be used for charging or powering the device as described inFIGS. 1 and 2. The integrated energy harvester can include varioussoftware-implemented modules, such as impedance matching 180, voltagerectifier 182, power management 184, battery 186, smart switch 188,micro-controller 190, channel estimator 192, feedback manager 194, querymanagement 196, registration/authentication 198, and energy updatemanager 199. The integrated energy harvester receives the energy beamsas well as ambient power and converts them from RF to DC. The harvestingprocess can be optimized by the power management module, whichreconfigures the impedance and rectifier parameters. The channelestimator can measure the channel periodically and forward these channelparameters to the feedback manger, where, based on previous channelstates and measured powers, precise feedback for ETs can be created. Thequery management module can handle the messages fromregistration/authentication, energy update, and feedback manager modulesfor energy requests, energy updates, and feedback.

FIG. 8 illustrates an adaptive resource allocation example of anET/device registration process. The controller parses all the incomingqueries using the query management module. If a registration message isdetected, the controller extracts the request type/ID which refers toeither an ET or a target device. Then, the controller registers the ETor the target device with its reported parameters that have beenincluded in the registration message, for example, accordingly into ahost table (for ETs) or a guest table (for devices). The controllersends an appropriate ACK to the ET or device to inform of a successfulcompletion of registration.

FIG. 9 depicts an embodiment of a process of adaptive energyallocations. The controller constantly monitors the registered devicesfor their change of energy discharging rates, rates of ambient RFharvesting, and battery levels utilizing the energy updates from thetarget devices. Each registered device through the RF energy harvestercan observe and monitor the level of ambient harvesting rate as well asbattery level.

When any of the monitored parameters goes below a specific threshold, anenergy request message can be initiated from the device to thecontroller. Such message contains the updated values of ambient energy,discharge rate, and battery level. The controller can classify thedevices based on their conditions into different priority levels. Itthen determines a set of ETs to serve the highest priority devices bychecking the energy transfer table. The energy transfer table containsthe end-to-end RF-to-DC conversion efficiency for each set of ETs anddevice. This number can be a function of a number of parametersincluding the distance between ETs and a target device, RF-harvestingcircuit, and transmission power.

In an initialization phase, the controller estimates these rates usingmeasured harvested powers that are reported from the devices. Afterupdating the best set of ETs and highest priority devices, thecontroller re-calculates the optimal energy beam-forming scheduling, andsends commands to ETs regarding their schedules/parameters.

FIG. 10 shows an embodiment of a process of adapting to any devicemovement and wireless channel change. Each ET can receive feedback fromits target device. This feedback can be utilized to estimate the channeland the arrival phase of signals transmitted between the ET and thedevice. The ET can determine any changes in the channel or locationchange of the target device through this estimated phase, and updatesthe feedback and steering matrices to provide continuous and accurateenergy beam forming. The ET can inform the controller about the newchanges and the energy transfer table can be updated accordingly.

FIG. 11 is an example embodiment of a distributed wireless chargingservice in an office or commercial building where the environment may bemore dynamic such that energy demands as well as the number ofactive/new devices change rapidly. The programmable ETs and targetdevices can connect to the controller at a server through an accesspoint (AP). The distributed ETs can be powered through a powerdistribution system and can be mounted or integrated to power outlets orstructures in the building such as in walls or ceilings. The targetdevices can register/authenticate to the wireless charging servicethrough the controller, and the distributed ETs can generate RF wavesthat combine constructively at a determined target device where theenergy beams can be harvested to power or charge the device as describedherein. Each target device, such as, without limitation, a phone, mouse,monitor, laptop, printer, voice recorder, shredder, projector, or anyother electronic device requiring a power input, can be coupled with anintegrated RF harvester. The controller can monitor the status of thewhole network by building energy maps, and can track the presence of thetarget devices by utilizing the distributed ETs that are located at thelocal network of devices. Energy demands of the target devices canchange over time, and new devices can join the energy network andexisting devices can leave. The controller can detect and manage thesechanges by sending new commands, including new energy waveconfigurations and beam scheduling, to the distributed ETs. Thecontroller can schedule ETs such that they sequentially change theirtarget devices over energy duty-cycles to charge multiple devices. Thecoverage and intensity of the wireless charging can depend on the numberof ETs. Additional ETs can be placed to reach greater distances, supporta greater number of targets, and achieve higher charging rates. Thecontroller can create groups of cooperative ETs, in which each group canhave a different set of target devices for distributed energybeamforming. The controller can change the role of an ET from energytransmitter to data access point, where an ET becomes responsible forcommunication and exchanges information through digital packetscompatible with specific wireless standards.

FIG. 12 is an example embodiment of software-defined distributedwireless charging system for a health application to power a network ofwearable computing devices. The devices can be implanted,surface-mounted on a body, carried on the person of a human subject viaembedding them in clothes or bags, or placed in a fixed location (e.g.,pill reminder). The devices can be coupled with integrated RF harvestersfor continuous monitoring and logging vital parameters. In thisembodiment, the continuous charging of devices when they move, witheither a low or high rate, can be a useful factor to provide safe andreliable health monitoring performances. The controller can manage thisissue through tracking of the devices by utilizing distributed ETs andcan adapt the power and scheduling of energy waves accordingly. The ETscan utilize feedback from the devices to adapt and adjust the phases ofenergy waves in order to combine all RF signals constructively at eachdetermined device.

FIG. 13 is another embodiment of a distributed wireless charging systemfor an IoT network in a smart home. A diverse set of smart sensorsassociated with target IoT devices, such as, without limitation, atemperature controller, soil monitor, toaster controller, smart lamp,watch, clock, TV/monitor, and notebook, can be connected through anaccess point (AP) with each other and a network such as the Internet.The controller can allocate the optimal energy streams, and thedistributed ETs can transmit energy waves accordingly, to createconstructive interference at sensors of each target device. Each targetdevice can be coupled with an integrated RF harvester, and can utilizethe beams of energy produced by the distributed ETs for charging orpowering the sensors. Besides the controlled energy beams, the IoTdevices can utilize ambient power from sources, such as an LTE network,GSM network, and digital TVs to charge or power the sensors. In thisembodiment, the power manager and energy scheduling modules in thecontroller, as described above, can leverage the more static behavior ofan IoT network and energy maps to anticipate and provide future energyneeds in advance.

In some embodiments, a distributed wireless charging system or methodcan include one or more of registration/authentication of a device to acontroller for receiving wireless energy services; resource allocationof energy beams and their schedules by a controller for distributedwireless energy transfer toward a set of given targets through sendingcommands from a controller to multiple spatially distributedprogrammable ETs; transmitting RF energy beams to form constructiveinterference at each determined target by multiple spatially distributedETs; converting energy contained in RF beams into DC storage byintegrating a smart energy harvester hardware with devices.

In some embodiments, a distributed wireless charging system or methodcan further include one or more of receiving ambient RF power, fromsources such as cellular and digital TV, besides the controlled energybeams, and converting them into DC power at the energy requesting deviceby the integrated energy harvester; and the integrated energy harvesterbroadcasting channel state information as well as energy updatefeedbacks to ETs and a controller.

In some embodiments, a distributed wireless charging system or methodcan further include the intelligent adaptation of energy waves based onchanges in available ambient powers as well as energy demands on thenetwork that are reported and measured by utilizing energy feedbacksfrom devices. These embodiments can further include the anticipatoryenergy scheduling with controller software based on learning a patternof energy usages/demands and estimating future energy needs in advance.These embodiments can still further include information such as energyrequest and energy updates from spatially distributed ETs beingintegrated in the controller software for accurate and reliable energyestimation and allocation.

In some embodiments, a distributed wireless charging system or methodcan further include modulating energy waves or shaping them into shortpulses in order to maximize the harvesting output powers. Theseembodiments can utilize the hardware-centric characteristics, such asRF-to-DC conversion efficiency curves of energy harvesters, to form theinput signals, accordingly.

In some embodiments, a distributed wireless charging system or methodcan further include the controller switching on and off ETs, andchanging their transmit power and transmit durations in order to extendor limit charging distance and charging rates of the system. Theseembodiments can further include localizing and tracking the locations ofdevices for reliable and continuous energy transfer in the applicationswith mobility such as health-care and also in dynamic environments withuser traffic, such as office/commercial buildings.

In some embodiments, a distributed wireless charging system or methodcan include switching between energy beamforming and wireless standardcompatible data communication modes, such as WiFi, ZigBee, andBluetooth, and determining schedules of switching, ETs that need tochange their roles, and data communication durations.

In some embodiments, a distributed wireless charging system or methodcan include controlling, allocating, and/or scheduling multiplespatially distributed ETs to beamform energy to a set of targets over agiven time.

In some embodiments, a distributed wireless charging system or methodcan include adapting wireless charging to the energy demands of thenetwork.

In some embodiments, a distributed wireless charging system or methodcan include anticipating future demands based on learning theusage/demand patterns.

In some embodiments, a distributed wireless charging system or methodcan include providing security, flexibility, and ease of use.

In some embodiments, a distributed wireless charging system or methodcan include integrating energy information (such as energy needs,updates, requests) from distributed devices in one place.

In some embodiments, a distributed wireless charging system or methodcan include commanding ETs to shape energy signals to maximize energyharvesting rates by utilizing energy harvesting circuit characteristics.

In some embodiments, a distributed wireless charging system or methodcan include leveraging ambient RF energy besides the controlled energybeams.

In some embodiments, a distributed wireless charging system or methodcan include accurately localizing a new device and tracking its locationand energy needs for reliable and continuous energy transfer.

In some embodiments, a distributed wireless charging system or methodcan include scheduling and commanding ETs to switch between energytransmitter and access point roles, and supporting data communicationswith devices that are equipped with wireless compatible standards radiotransceivers.

The wireless charging system and method described herein can be used ina variety of applications. For example, the wireless charging marketincludes small-factor, battery-powered electronic devices that can beused for personal (consumer market), business (industrial/commercialmarkets), and military uses. Market segments for wireless charging caninclude homes, hotels/hospitality, military, malls, coffee shops,restaurants, hospitals, factories, vehicles, and smart cities.Applications of embodiments of this invention can include, but are notlimited to, equipment in commercial buildings, offices and sensors inindustrial machine floors, Internet of Things (IoT) enabled devices andappliances, and health-care.

By way of further examples, in the healthcare field, wireless chargingcan be used for medical and wearable devices, in-body as well ashealth-related electronic devices outside the body. In the automotivefield, wireless charging can be used for electronic devices inside avehicle. In commercial buildings, wireless charging can be used forelectronic devices such as laptops, smart-phones, and sensors insideoffice/commercial buildings. In restaurants & coffee shops, wirelesscharging can be used for electronic devices such as smart-phones andlaptops. In a smart city, wireless charging can be used for a variety ofsensors, for example, to monitor the structural health ofbuildings/bridges, to monitor roads, lighting, waste management, waterquality, air pollution, and the like. In a smart home, wireless chargingcan be used for electronic devices such as laptops and smart phones, aswell as for a variety of sensors that can be utilized in a home, such asof remote control sensors and switches, lamps, watches, temperaturecontrollers, smoke alarms, electric toothbrushes, and the like.

Embodiments of the technology described herein can provide variousadvantages. For example, embodiments can ensure that devices remainoperational for longer times, increase reliability, save time, savemoney, provide freedom from the location constraints of wired charging,eliminate the efforts of battery replacements, realize thenext-generation wireless-powered IT infrastructure, and eliminate theefforts for wired-charging hardware installations. The technology canincrease revenue and customer experience for businesses that provide awireless charging service to customers or guests. End users cancustomize and visually monitor the performance of the ongoing chargingprocess.

The system and method can provide higher levels of adaptation andconfigurability for wireless charging through a software-definedarchitecture with controller software and programmable ETs.

The system and method can provide higher wireless charging rates as wellas charging distances through spatially distributed wireless beamformingcompared to omni-directional RF energy transfer.

The system and method can provide greater flexibility, security, andease of use through integrated and centralized management, distributedenergy transfer, intelligent adaptations, and learning-basedestimations.

The system and method can provide efficient and high levels of RFharvesting through inclusion of an integrated multi-band harvester thatcaptures and adapts to both ambient and controlled energy beams.

The system and method do not need a tight alignment between the chargersand the target devices, or short-contacts as in the case ofnon-radiative coupling-based charging technologies, such as inductivecoupling, magnetic resonance coupling, and capacitive coupling.

The system and method can provide higher reliability and scalability fordynamic and mobile applications.

The system and method can provide enhanced functionality by supportingboth wireless charging and wireless standard compatible datacommunications.

The system and method can enhance data communication interoperabilitybetween devices through programmable energy transmitters that act asaccess point and support different wireless standards, for example,WiFi, ZigBee, and Bluetooth.

In some embodiments as used herein, “software-defined beamforming” mayrefer to controlling the phase, frequency, duration, direction, andpower of energy beams from distributed programmable ETs through a remotesoftware controller, which has access to the integrated energy and dataknowledge of network through a network connection. “Distributed energycharging” may refer to a process of generating two or more RF waves thatconstructively combine at an intended receiver from physically separatedETs. In the case of multiple receivers, the waves may be scheduled overtime to sequentially cover all energy requesting devices from the targetset. “Programmable ET or PET” may refer to a wireless charger thattransmits high power RF waves, and is equipped with software-definedradios, so that it may be reconfigured through commands from thesoftware controller. “Software manager/controller” may refer to acontroller that performs the overall messaging and control operationsspanning device registration to fine-grained tuning of the ET operation.It adaptively and remotely manages the construction and emission of theenergy waves and their schedules based on the energy needs of thenetwork. “Anticipatory energy scheduling” may refer to configuringenergy waves such that they can provide adequate power to supportestimated future node operations. “Smart energy harvester” may refer toa multi-band RF harvester with an integrated smart switch that allowsharvesting of energy beams as well as selection of one or more specificambient bands of interest based on available channels and spectral powerlevels adaptively. It also provides efficient and sharp rectification ofsignals from a single source with the highest power. In various examplesdescribed herein, the “receiver” generally includes a device connectedto the energy harvester. “Device registration” may refer to a process ofregistration and authentication of an energy requesting target devicewith the controller in order to receive wireless energy delivery. “Liveenergy maps” may refer to dynamic updating maps of energy levels ofdevices in the network that may be utilized to estimate the futureenergy demands as well as present a visualization of the energy statusof the devices for an end-user. “Energy update” may refer to packetsfrom a device to the software controller that updates the status of itstraffic rates as well as level of energy, and may include otherenergy-related fields. “Switching modes” may refer to two processes: (i)the process of switching from the role of energy transmitted to the dataaccess point, and transmission of data packets based on a wirelessstandard such as WiFi, ZigBee, and Bluetooth; (ii) the process ofswitching from data access point to the role of energy transmitter, andbeamforming energy. “Transceiver” may include one or more devices thatboth transmit and receive signals, whether sharing common circuitry,housing, or a circuit board, or whether distributed over separatedcircuitry, housings, or circuit boards, and can include atransmitter-receiver.

The software provided to perform the example operations within theembodiments disclosed herein may be any computer-readable instructionsconfigured to cause a processor or apparatus to perform the exampleoperations. The instructions may be stored on any non-transitory,computer-readable medium, and, when loaded and executed by a processor,causes the processor or associated apparatus to perform the exampleoperations.

The controller, energy transmitters, and energy harvesting targetdevices can be part of a computer system(s) that executes programmingfor controlling the system for wireless charging as described herein.The computing system(s) can be implemented as or can include a computingdevice that includes a combination of hardware, software, and firmwarethat allows the computing device to run an applications layer orotherwise perform various processing tasks. Computing devices caninclude without limitation personal computers, work stations, servers,laptop computers, tablet computers, mobile devices, hand-held devices,wireless devices, smartphones, wearable devices, embedded devices,microprocessor-based devices, microcontroller-based devices,programmable consumer electronics, mini-computers, main frame computers,and the like.

The computing device can include a basic input/output system (BIOS) andan operating system as software to manage hardware components,coordinate the interface between hardware and software, and manage basicoperations such as start up. The computing device can include one ormore processors and memory that cooperate with the operating system toprovide basic functionality for the computing device. The operatingsystem provides support functionality for the applications layer andother processing tasks. The computing device can include a system bus orother bus (such as memory bus, local bus, peripheral bus, and the like)for providing communication between the various hardware, software, andfirmware components and with any external devices. Any type ofarchitecture or infrastructure that allows the components to communicateand interact with each other can be used.

Processing tasks can be carried out by one or more processors. Varioustypes of processing technology can be used, including a single processoror multiple processors, a central processing unit (CPU), multicoreprocessors, parallel processors, or distributed processors. Additionalspecialized processing resources such as graphics (e.g., a graphicsprocessing unit or GPU), video, multimedia, or mathematical processingcapabilities can be provided to perform certain processing tasks.Processing tasks can be implemented with computer-executableinstructions, such as application programs or other program modules,executed by the computing device. Application programs and programmodules can include routines, subroutines, programs, scripts, drivers,objects, components, data structures, and the like that performparticular tasks or operate on data.

Processors can include one or more logic devices, such as small-scaleintegrated circuits, programmable logic arrays, programmable logicdevice, masked-programmed gate arrays, field programmable gate arrays(FPGAs), and application specific integrated circuits (ASICs). Logicdevices can include, without limitation, arithmetic logic blocks andoperators, registers, finite state machines, multiplexers, accumulators,comparators, counters, look-up tables, gates, latches, flip-flops, inputand output ports, carry in and carry out ports, and parity generators,and interconnection resources for logic blocks, logic units and logiccells.

The computing device includes memory or storage, which can be accessedby the system bus or in any other manner. Memory can store controllogic, instructions, and/or data. Memory can include transitory memory,such as cache memory, random access memory (RAM), static random accessmemory (SRAM), main memory, dynamic random access memory (DRAM), andmemristor memory cells. Memory can include storage for firmware ormicrocode, such as programmable read only memory (PROM) and erasableprogrammable read only memory (EPROM). Memory can include non-transitoryor nonvolatile or persistent memory such as read only memory (ROM), harddisk drives, optical storage devices, compact disc drives, flash drives,floppy disk drives, magnetic tape drives, memory chips, and memristormemory cells. Non-transitory memory can be provided on a removablestorage device. A computer-readable medium can include any physicalmedium that is capable of encoding instructions and/or storing data thatcan be subsequently used by a processor to implement embodiments of themethod and system described herein. Physical media can include floppydiscs, optical discs, CDs, mini-CDs, DVDs, HD-DVDs, Blu-ray discs, harddrives, tape drives, flash memory, or memory chips. Any other type oftangible, non-transitory storage that can provide instructions and/ordata to a processor can be used in these embodiments.

The computing device can include one or more input/output interfaces forconnecting input and output devices to various other components of thecomputing device. Input and output devices can include, withoutlimitation, keyboards, mice, microphones, displays, touchscreens,monitors, scanners, speakers, and printers. Interfaces can includeuniversal serial bus (USB) ports, serial ports, parallel ports, and thelike.

The computing device can access a network over a network connection thatprovides the computing device with telecommunications capabilities.Network connection enables the computing device to communicate andinteract with any combination of remote devices, remote networks, andremote entities via a communications link.

The computing device can include a browser and a display that allow auser to browse and view pages or other content served by a web serverover the communications link. A web server, server, and database can belocated at the same or at different locations and can be part of thesame computing device, different computing devices, or distributedacross a network. A data center can be located at a remote location andaccessed by the computing device over a network.

The computer system(s) can include architecture distributed over one ormore networks, such as, for example, a cloud computing architecture.Cloud computing includes without limitation distributed networkarchitectures for providing, for example, software as a service (SaaS),infrastructure as a service (IaaS), platform as a service (PaaS),network as a service (NaaS), data as a service (DaaS), database as aservice (DBaaS), desktop as a service (DaaS), backend as a service(BaaS), test environment as a service (TEaaS), API as a service(APIaaS), and integration platform as a service (IPaaS).

EXAMPLES Example 1

A prototype implementation was developed to demonstrate distributedenergy beamforming to power sensor nodes. FIG. 14A shows the prototypesetup, which included two programmable ETs, an RF-energy harvestercircuit, and a controller. The programmable ETs were each based on aUniversal Software Radio Peripheral (USRP) B210, manufactured by EttusResearch LLC, as a software-defined radio connected to a poweramplifier. The USRPs were controlled with the open source USRP hardwaredriver (UHD), and GNURadio software. The prototype included featuressuch as frequency synchronization, phase synchronization, and phaseadjustments for forming constructive energy beams, as described above.The RF-energy harvester was fabricated and connected to a sensor device(TI EZ430) to convert RF-to-DC with high efficiency.

The RF energy harvesting circuit included an antenna, an impedancematching network sub-circuit, a 4-stage diode-based Dickson voltagerectifier, and a 3300 μF capacitor for energy storage. The impedancematching network sub-circuit with adjustable capacitors maximized theenergy transfer and minimized power reflection between the antenna andthe voltage rectifier. For efficient DC conversion, a 4-stagediode-based Dickson voltage rectifier was designed by choosing aSchottky diode that operates with quick activation time and lowerforwarding voltage drop as the nonlinear component of rectifier. The3300 μF capacitor was used to store the energy from the voltagerectifier, which served as the energy storage for operating the TI EZ430sensor.

The GnuRadio software plane in the USRPs implemented the beamformingalgorithm for phase and frequency synchronizations, and transferred highpower energy signals toward the desired receiver at the energy harvestercircuit using a power amplifier with maximum allowable power under FCCrules. Using distributed energy beamforming, the ETs were able toself-adjust their phase based on feedback from the receiver, so thatmaximum net energy was transferred towards the intended receiver. Inparticular, the ETs were able to organize themselves into a virtualantenna array and focus their transmission energy in the direction ofthe sensor device, such that the emitted waveforms added upconstructively at the target sensor. Each ET also used an extendedKalman filter to estimate and correct the frequency offset between itscarrier frequency and the feedback as reference signal.

FIG. 14B shows the results of the energy beamforming for two ETs, andimprovements of the received power. The net conversion efficiencydepends upon the accurate phase matching of the ETs and the circuitdesign. Once the voltage across the capacitor reached 3.6V, the sensorsdisconnected from the charging phase and resumed their normal operation.FIG. 14B shows the amplitude of received power for 4 cases: the first ET(ET1) was on, the second ET (ET2) was on, both ETs were on, but nodistributed beamforming had been implemented, and finally two ETs wereon with distributed beamforming. The results show the improvement ofthis method and system on the received power and also depict thedurations that initial synchronization needed.

FIG. 14C shows the instantaneous harvested voltage that was measured atthe output of RF energy harvesting circuit for (a) beamforming-enabledand (b) beamforming-disabled scenarios. It shows the level of harvestedvoltage when only one ET is turned on, and then two ETs aretransmitting. The consistency of constructive interference in the caseof the present beamforming-enabled implementation is demonstrated. Theprototype implementation included a middleware developed to contain thesoftware controller and communicate with both USRPs and sensor receiversfor optimal managing of the hardware resources and scheduling. Thecontroller included a Python-based control plane based on the Twistedframework. The controller accepted registration beacons emitted by thesensors and ETs. Each beacon contained not only the unique device ID,but also a description of the functions supported by the discovereddevice in a pre-determined format.

The USRP hardware driver was modified for the USRP devices toautomatically transmit these beacons, if the device was not alreadyregistered. Twisted ran two reactor loops at both ends of theET/sensor-controller connection, allowing each device to accept higherlevel directives as and when they arrived, while also allowing thecontroller to receive energy requests from the sensors. The controllerthen executed remote procedural calls, wherein it invokes specificfunctions in the ETs (such as tuning the center frequency and startingthe beamforming algorithm) based on the incoming energy requests.

Example 2

As noted above, FIG. 3 illustrates two-dimensional patterns oftransferred energy produced by multiple ETs. Concurrent energytransmissions at the same frequency cancel the transferred energy indestructive areas and aggregate energy in constructive areas. Throughexperimental measurements, FIG. 15 illustrates the effects ofconstructive and destructive combinations of energy waves from two ETs.Here, the two ETs transferred energy with random initial phases at 915MHz each with an output power of 3 Watts. The ET and RF energyharvesting circuits had antenna gains of 1 dBi and 6.1 dBi,respectively, and the capacitor storage of the receiver node was C=100mF. The total harvested power was measured while varying the distancesbetween energy transmitters and the receiver, which led to the differentphase separations of the arriving energy waves. It can be observed thatdestructive interference from one ET strongly affected the energytransmitted by another ET, and at distances, all transmitted energywaves could be canceled totally. This resulted in very low or noharvested power even when all ETs were transferring energy with highpower.

Example 3

A prototype of a dual-stage RF energy harvesting device was developed,illustrated in FIG. 16, for operation in both low power and high powerregions. The prototype of the dual-stage energy harvesting circuit wasbased on the voltage multiplier. The prototype was designed consideringall input parameters needed to obtain high power conversion efficiencyfrom the RF energy harvester. The main components of prototype andparameters that influenced the efficiency and performance of the circuitincluded the multiplier topology, nonlinear components of themultiplier, and the number of stages.

The multiplier topologies do not demonstrate a significant difference inperformance. Hence, a Dickson topology (FIG. 17), which has a parallelconfiguration of capacitors in each stage, was chosen. This topology wasadvantageous in this implementation because with the capacitorsconnected in parallel, the effective circuit impedance was reduced. Thismade the task of matching the antenna side to the load side simpler.

The nonlinear components of the multiplier can be selected to enable theenergy harvesting circuit to operate with weak input RF power. As thepeak voltage of the RF signal obtained at the antenna is generally muchsmaller than the diode threshold, diodes with the lowest possible turnon voltage are preferable. Moreover, since the energy harvesting circuitis operating in high frequencies, diodes with a very fast switching timeare preferred. Schottky diodes use a metal-semiconductor j unctioninstead of a semiconductor-semiconductor junction. This allows thejunction to operate much faster, and gives a forward voltage drop of aslow as 0.15V. The prototype employed two different diodes from AvagoTechnologies, HSMS-2822 and HSMS-2852. The former has a turn on voltageof 340 mV while the latter is at 150 mV, measured at 1 mA and 0.1 mA,respectively. Consequently, HSMS-2852 was suitable for the low powerdesign (LPD) used in the weak RF environment, while HSMS-2822 waspreferred for the high power design (HPD) in the strong RF environment.

The number of multiplier stages is influential on the output voltage ofthe energy harvesting circuit. Each stage in this prototype was amodified voltage multiplier, arranged in series. The output voltage wasdirectly proportional to the number of stages used in the energyharvesting circuit. However, practical constraints forced a limit on thenumber of permissible stages, and in turn, the output voltage. Here, thevoltage gain decreased as number of stages increased due to parasiticeffect of the constituent capacitors of each stage, and finally itbecame negligible. Due to this, a 7-stage low power region and a10-stage high power region were chosen with the crossover point of 10.75dBm, to yield the maximum efficiency.

The printed circuit board (PCB) of the dual stage RF energy harvestingprototype was connected to a Mica2 mote (shown in FIG. 19). The PCB wasfabricated with FR-4 epoxy glass substrate and had two layers, one ofwhich served as a ground plane. The prototype components and values aresummarized in Tables 1 and 2.

TABLE 1 Components for dual-stage circuit design Component ValueInductor 3.0, 7.12 nH Capacitor 1.5, 2.9 pF Stage capacitor 36 pF DiodeHSMS-2852, HSMS-2822

TABLE 2 Parameters used in the PCB fabrication for dual-stage circuitdesign Component Value Laminate thickness 62 mil. FR-4 Number of layers2-layer, one serves as a ground plane Copper thickness 1.7 mil. Tracewidth 20 mil. with 12 mil. gap Dielectric constant 4.6 Through-hole size29 mil.

This prototype was able to continuously operate Mica2 sensor motes whentheir duty-cycle was selected based on the incident RF power (as low as−6 dBm). Moreover, this prototype was able to sustain the energy neutralof Texas Instruments' MSP430G2553 in LPM4 at −20 dBm. In comparisonsbetween the efficiency of this prototype with that of the commerciallyavailable RF energy harvester from Powercast P1100, this prototypelargely outperformed the Powercast P1100 in the range of −20 to −7 dBm.

Example 4

A prototype was provided as an adjustable ambient RF harvesting circuitto enable efficiently harvesting available energy from LTE 700, GSM 850,and ISM 900 bands with a single energy harvesting circuit. FIG. 18schematically illustrates the components of the ambient energyharvesting circuit. The voltage multiplier included a 4-stage Dicksonvoltage multiplier and zero bias Schottky diode HSMS-285C to convert theincident ambient RF power into functional DC power. The impedancematching network was a modified π tunable impedance network that allowedadjustable selection of the excited frequency band according toavailable ambient power, such that it provided the maximum powerdelivery from the antenna to the voltage multiplier at the excitedfrequency band. The energy storage established the load smooth DC powerdelivery.

FIG. 19 shows the PCB of the ambient RF energy harvesting circuitprototype. The PCB board was designed with two layers, one of whichserved as a ground plane and was fabricated with FR-4 epoxy glasssubstrate. The circuit architecture and circuit components andparameters were selected according to design challenges that affectcircuit performance discussed above in Example 3. The prototype used a4-stage Dickson voltage multiplier composed of zero bias Schottky diodeHSMS-285C, which has same specifications as the HSMS-2852, such as theturn-on voltage of 150 mV measured at 0.1 mA, with a smaller packagesize. In order to optimize the impedance matching network in thecircuit, the adjustable capacitors were trimmed by using an AgilentE5061B vector network analyzer with determined ambient frequency rangeand RF input power level. Consequently, the prototype was tunable to theambient signal frequency bands such as LTE 700 (734-756 MHz), GSM 850(869-894 MHz), and ISM 900 (902-928 MHz) bands, allowing the prototypeto effectively target these bands to harvest their ambient RF energy.The configuration of the prototype is summarized in Table 3.

TABLE 3 Components used in fabrication for ambient RF energy harvestingcircuit Circuitry Topology Component Value Multiplier Dicksondiode-based Diode HSMS-285C Four Stage Stage Capacitor 100 pF ImpedanceAdjustable-configured Shunt Trimmer 1 2.2-22 pF Matching NetworkModified π network Shunt Trimmer 2 3-36 pF Energy Storage Capacitor 3300μF

The prototype was able to constantly operate a TI eZ430-RF2500 sensor inbattery-less operation mode at different environmental locations ofBoston with power conversion efficiencies of up to 45% at LTE 700, GSM850, and ISM 900 bands. Moreover, the prototype was able to operateextremely low-power Texas Instruments' microcontroller units such asMSP430L092 and MSP430G2553 in different operation modes for example,active, standby and LPM4 mode at input RF power range between −25 and −5dBm.

Example 5

In order to study and demonstrate the feasibility of harvesting ambientRF power, an RF spectral survey at GSM850, GSM1900, LTE730, LTE740, andDTV bands was conducted within the Boston area in Massachusetts. Theambient spectrum studies were undertaken from outside of 40 subwaystations at street level as survey points that are distributed in thecity to measure the available RF power within each ambient band. A USRP2device with a WBX antenna manufactured by Ettus Research LLC was used,and it was calibrated in the laboratory with an Agilent N9000 signalanalyzer. The percentages of each ambient RF signal band in which thehighest power are measured over all locations were calculated as 46%,5%, 30%, 16% and 3% for GSM850, GSM1900, LTE730, LTE740, and DTV,respectively as seen in FIG. 20. This implies that 92% available ambientRF power is covered by LTE700 and GSM850 bands. The banded input RFpower in mW was calculated by summing and averaging over all receivedpower across the band in a similar way the spectrum analyzer calculateschannel power. Table 4 summarizes the results across all subway stationsindicating the frequencies, average, maximum, median, and standarddeviation for all banded power measurements. It can be observed that RFambient powers can be relatively high and suitable for harvesting. Inaddition, FIG. 21 illustrates the spatial diversity of ambient powersover seven Boston subway stations, which is also an indication of theadvantage and usability of available RF ambient power in addition tocontrolled beams, especially in applications with longer requiredperiods of charging.

TABLE 4 Band GSM850 GSM1900 LTE730 LTE740 DTV Frequencies (MHz) 869-8941930-1950 734-744 746-756 494-584 Average (mW) 1.8153 0.1335 1.41931.4029 0.0547 Maximum (mW) 10.3474 0.5226 13.0601 19.1625 0.3038 Median(mW) 0.7938 0.0821 0.2869 0.0825 0.0362 StDev 2.4500 0.1351 2.98763.5793 0.0610

Based on this ambient RF survey, FIGS. 22A and 22B compare the chargingtimes needed to power a Nordic nRF51822 low-energy Bluetooth radio fortransmission of one packet in three scenarios: i) ET wireless transferwithout any ambient harvesting, ii) ET wireless transfer with ambientharvesting at LTE 730 MHz, and iii) ET wireless transfer with ambientharvesting at GSM 850 MHz. FIG. 22A illustrates the charging timecomparisons for different distances of ET to receiver device, when ETEffective Isotropic Radiated Power (EIRP) is equal to 1. EIRP is thetotal effective radiated power from an antenna, which includestransmitted power, gains that the antenna provides, and losses from theantenna cable. In addition, FIG. 22B compares the charging times ofmentioned scenarios for different EIRPs when distance from the ETs tothe receiver is set to 2m.

In the light of initial RF survey, for the next step, the availableambient RF power at LTE700 and GSM850 bands was measured using theprototype of Example 4 within six different locations in Boston, auniversity, a museum, a shopping center, outside of a subway station, apark, and a concert theater. These particular locations were selected tohelp comprehend the disparities and similarities among results in termsof geographical terrain and population distribution and density wheninvestigating energy level in such environments. Table 5 gives a reviewof the locations where experiments were done. The measurement sampleswere obtained with a 30-minute section at each location and each sectionwas repeated at the same time and same location for 5 days. Usingdataset from survey of signal strength distribution in Boston, FIG. 23depicts levels of average ambient RF power at determined frequenciesover a set of locations with maximum and minimum levels of ambient RFpower. This indicates that more that 65% of determined locations inBoston have enough RF power density to operate a low-power sensor motein a battery-less operation mode.

TABLE 5 Statistical summary of available ambient RF powers over BostonIndex Location Experimental Name Description Time-line Frequency Band μ(dBm/s) σ (μ) MFA-1 Museum of Fine Jul. 26, 2016-Jul. 30, 2016 LTE (734MHz-756 MHz) −6.7 1.818 Arts; outdoor MFA-2 Museum of Fine Aug. 1,2016-Aug. 5, 2016 GSM (869 MHz-894 MHz) −6.9 2.017 Arts; outdoor EllHall-1 Northeastern University, Jul. 26, 2016-Jul. 30, 2016 LTE (734MHz-756 MHz) −8.7 0.284 Krentzman Quadrangle; outdoor Ell Hall-2Northeastern University, Aug. 1, 2016-Aug. 5, 2016 GSM (869 MHz-894 MHz)−4.5 0.286 Krentzman Quadrangle; outdoor Symphony-1 Symphony Hall;outdoor Aug. 3, 2016-Aug. 7, 2016 LTE (734 MHz-756 MHz) −7.5 0.959Symphony-2 Symphony Hall; outdoor Aug. 8, 2016-Aug. 12, 2016 GSM (869MHz-894 MHz) −6.7 0.883 Prudential-1 Prudential Tower; outdoor Aug. 8,2016-Aug. 12, 2016 LTE (734 MHz-756 MHz) −18.3 1.308 Prudential-2Prudential Tower; outdoor Aug. 12, 2016-Aug. 14, 2016 GSM (869 MHz-894MHz) −13.3 0.851 Arlington-1 Arlington, near the Aug. 15, 2016-Aug. 19,2016 LTE (734 MHz-756 MHz) −22.1 0.468 subway station; outdoorArlington-2 Arlington, near the Aug. 15, 2016-Aug. 19, 2016 GSM (869MHz-894 MHz) −24.7 0.338 subway station; outdoor Boston Common-1 BostonCommon Aug. 16, 2016-Aug. 20, 2016 LTE (734 MHz-756 MHz) −8.3 0.21Public Park; outdoor Boston Common-2 Boston Common Aug. 16, 2016-Aug.20, 2016 GSM (869 MHz-894 MHz) −5.5 0.143 Public Park; outdoor

Example 6

The system and method can provide higher wireless charging rates as wellas charging distances through spatially distributed wireless beamformingcompared to omni-directional RF energy transfer. FIG. 24A illustrates acomparison of the maximum charging ranges between FDMA (i.e.omni-directional energy transfer at different frequencies) and energybeamforming, when the minimum input power for the RF harvesting circuitis −5 dBm. It demonstrates the significant increase of charging rangewhen beamforming is utilized as described herein. On the other hand,FIG. 24B illustrates the harvesting rates that resulted from energybeamforming in comparison with FDMA, when ETs were placed at a distanceof two meters. The improvements in harvesting rates due to beamformingas the Effective Isotropic Radiated Power (EIRP) increased can be seen.It is noteworthy that the energy transfers at the same frequency withoutbeamforming resulted in random destructive interference.

As used herein, “consisting essentially of” allows the inclusion ofmaterials or steps that do not materially affect the basic and novelcharacteristics of the claim. Any recitation herein of the term“comprising,” particularly in a description of components of acomposition or in a description of elements of a device, can beexchanged with “consisting essentially of” or “consisting of.”

It will be appreciated that the various features of the embodimentsdescribed herein can be combined in a variety of ways. For example, afeature described in conjunction with one embodiment may be included inanother embodiment even if not explicitly described in conjunction withthat embodiment.

To the extent that the appended claims have been drafted withoutmultiple dependencies, this has been done only to accommodate formalrequirements in jurisdictions which do not allow such multipledependencies. It should be noted that all possible combinations offeatures which would be implied by rendering the claims multiplydependent are explicitly envisaged and should be considered part of theinvention.

The present invention has been described in conjunction with certainpreferred embodiments. It is to be understood that the invention is notlimited to the exact details of construction, operation, exact materialsor embodiments shown and described, and that various modifications,substitutions of equivalents, alterations to the compositions, and otherchanges to the embodiments disclosed herein will be apparent to one ofskill in the art.

What is claimed is:
 1. A method for distributed wireless charging,comprising: in a network comprising at least two spatially distributedenergy transmitters, a plurality of energy receiving target devices, anda controller comprising one or more processors and memory, and machinereadable instructions stored in the memory executable by the one or moreprocessors, the steps of, at the controller: receiving a communicationfrom at least one energy receiving target device or from one of theenergy transmitters comprising a need for energy by one or more of theenergy receiving target devices; transmitting to the at least two energytransmitters, instructions for wireless transmission of radio frequency(RF) energy from the at least two energy transmitters to formconstructive interference at an identified energy receiving targetdevice, wherein the at least two energy transmitters are operative tocoordinate adjustment of one or more of a frequency, a phase, and a timeof transmission of the RF energy to form constructive energy beams atthe identified energy receiving target device; and transmitting, to atleast one of the energy transmitters, configuration commands to switchbetween an energy transmission mode and an active data communicationmode, including an identification of the energy transmitter to switchmodes, a schedule of switching modes, a duration in each mode, and awireless data communication protocol for use in the active datacommunication mode; wherein each of the energy transmitters comprises asoftware-defined radio configurable by communications from thecontroller, and an antenna in communication with the software-definedradio, and each of the energy transmitters is switchable between theenergy transmission mode and the active data communication mode usingthe wireless data communication protocol for the network.
 2. The methodof claim 1, wherein each of the energy transmitters further includes acommand manager module operative to receive and process commands fromthe controller, and a data manager module operative to exchange digitaldata packets with the controller and others of the energy transmittersand the energy receiving target devices according to the wireless datacommunication protocol when in the active data communication mode. 3.The method of claim 1, wherein one or more of the energy transmittersfurther comprise a data access point or a gateway for the network.
 4. Anenergy transmitter device comprising: a software-defined radio; anantenna in communication with the software-defined radio; and a commandmanager module operative to receive and process commands from anexternal controller, wherein the device is operative as a data accesspoint or a gateway for a network.
 5. The device of claim 4, furthercomprising: a data manager module operative to exchange digital datapackets with the external controller and other external energytransmitters devices, according to the wireless data communicationprotocol when in an active data communication mode; and an energy wavemanager operative to adjust one or more of a frequency, a phase, and atime of transmission of RF energy to form constructive energy beams atan energy harvesting target device and is operative to optimizeconstructive interference at the energy harvesting target device inresponse to the feedback, by iteratively adjusting one or more offrequency, phase, or timing of the RF energy; wherein the device isswitchable between an energy transmission mode and the active datacommunication mode using a wireless data communication protocol for thenetwork.